The present invention relates generally to an improved bypass and unloader valve, and more particularly to such a valve structure having improved design features, including inlet and outlet port disposition, and sealing and guide arrangements for the check valve unseating stem. In the past, bypass and unloader valve structures have been provided which function in a fashion similar to that of the present device, however these devices have presented some unusual production and machining requirements, and the finished products have frequently encountered problems due to guide and seal arrangements.
Bypass and unloader valves are particularly desired for high pressure fluid systems which employ a discharge which is intermittently shut off. Typically, such systems are employed for liquid high pressure sprayers and washers, although a variety of other applications are, of course, common. When the system is equipped with an unloader valve, the discharge may be completely shut off without stopping or interrupting the operation of the pump itself.
By incorporating the bypass feature, a partial bypass may be provided in instances where the discharge is only partially closed or, if the orifice in the outlet becomes restricted so that the capacity of the pump may not be discharged under the normal conditions. In the event of such an occurrence, pressure will increase in the discharge line, and the bypass feature of the combined bypass and unloader valve will operate to effect a partial bypass of the liquid being pumped. When the discharge is closed the unloader functions to completely bypass the entire output of the pump, thus achieving unloading of the entire pump capacity. Upon opening of the discharge, the function of the valve is to close the bypass and restore normal flow conditions and operation.
While these operations are typical for bypass and unloader valve combinations, and while these devices have been available in the past, problems have developed in their manufacture and use due to unusual design configurations and difficult guide and seal functions which normally are present. With regard to unusual design configurations, the inlet and outlet ports have normally been arranged in other than coaxial disposition, and such a positioning of these ports and the bores associated therewith have resulted in a relatively expensive machining operation. Also, the configuration has been such that substantial pressure losses are encountered during periods of normal flow, and such pressure losses are, of course, deemed undesirable. The present arrangement provides for coaxially disposed inlet and outlet ports, along with the bores which interconnect these ports. The design is such that very little, if any, pressure drop occurs during normal periods of flow.
The valve utilizes a variable spring biased plunger mounted on a stem in a discharge chamber, the plunger having its inner end disposed to unseat a check valve in the system upon lifting of the plunger. In order to achieve proper biasing, a relatively long helical spring is desired, with the spring force being adjustable and designed to provide the required bias. The length of the spring determines, at least in part, the axial length requirement of the stem upon which the plunger is mounted. As is conventional, this stem is received in a stuffing box and is equipped with stem seals. Because of the reciprocatory motion of the stem within the assembly, and the length thereof, problems have been encountered in the past with leakage in the stuffing box and the stem seal area. Also, guiding has occasionally presented some problems with the stuffing box normally providing the guiding function.